1. Field of the Invention
The present invention relates to a method for providing brazing alloy on detailed parts in an exact pattern of the joints to be brazed.
2. Description of the Prior Art
Brazing, as well as soldering, is based upon the close juxtaposition of metal pieces so that inter-atomic attraction will bind them together in permanent metallic bond when the metals to be joined are wetted with molten metal and cooled. The basic brazing and soldering techniques and equipment are similar for use in joining all metals, with variations depending upon the particular metal or combination of metals involved.
For aluminum and its alloys, for which the present invention has particular application, the general brazing procedure includes the following steps. The surfaces to be joined are cleaned, and spaced from one another a few thousandths of an inch. Brazing filler or solder is placed in the joint area of the part to be joined, a suitable flux is added and heat is applied. The flux reacts, displaces the oxide on the surface of the base metal, and shields the bare metal from contact with the air. In vacuum brazing, the flux is omitted. The brazing filler metal melts and is drawn into the joint by capillary attraction. The flowing brazing metal displaces the flux and wets the hot base metal which upon cooling, forms the joint. For further description of several brazing methods and relevant brazing information, reference is made to the "Aluminum Brazing Handbook", first edition, January 1971, published by The Aluminum Association, 750 Third Avenue, New York, N.Y. 10017, Library of Congress Catalog Card Number 71-159578.
For complicated joints, such as found in power dividers and waveguides, it is conventional to use brazing foil, which is cut and positioned between the joints at the time of assembly, and/or to place brazing wire and paste along each joint, or to use a brazing sheet with its entire surface clad with brazing alloy, even in places where the alloy is not needed. This latter use of cladding generally is unacceptable not only because excess brazing alloy results in waste but also, and more importantly, because the presence of the excess brazing alloy may prevent proper operation of the brazed device, whether its operation is electrical or otherwise. Generally, it is impossible, or at least impractical, to remove such excess brazing alloy. The former two techniques of utilizing foil and/or wire and paste require expensive hand fitting of the brazing alloy to the joints so that it is placed exactly and only where needed. Handling requires cleaning and degreasing of parts. Even in such instances of using brazing foil, for example, 100% electrical tests of each power divider is required due to manufacturing imperfections which arise from voids and skips occuring in unbrazed areas. Such voids and skips result from problems in placement of the brazing foil as well as from differences in the amount or thickness of the brazing material used. Such skips may result in corrosion from galvanic action if moisture enters the device.